The technology to express and utilize money or information having monetary value such as electronic money or electronic ticket in the electronic format has recently grown up as the ordinary technology. Electronically expressed value information such as electronic cash or electronic ticket will be called later as electronic value information.
As a method of expression, an electronic value information is set on a server installed in distant area and an owner of this electronic value information has only an authentication information and makes communication with the server at the time of application. This method however has a problem that safe transaction can be realized by assuring sufficient safety in the authentication but electronic value information can be used only in the condition that the system may be connected to the network and also has a problem that inquiry to the network is generated for each application and thereby it is difficult to adapt this method to the condition that requires high speed response.
Therefore, in view of utilizing the electronic value information even under the condition that is independent of the network, there has been proposed a technique for holding electronic value information itself on devices such as IC card, hand-held telephone set and hand-held terminal carried by an owner of electronic value. However, in this case, there is a risk of losing electronic value information due to destruction and missing of devices.
In order to realize recovery from the problem of destruction of electronic information including electronic value information explained above, several technologies have already been proposed. Examples of such prior arts will be explained below.
In the technology disclosed in the JP-A No. H10-133925 as the first related art, data can be backed up for the backup server installed at the outside of fire wall from the inside thereof by utilizing an encrypted mail. However, in this technique, a recovery method from the encrypted data when the key is lost or broken is not considered.
In the technology disclosed in the U.S. Pat. No. 5,778,395 as the second related art, files of node (computer) connected to the network are backed up through compression and encryption to the server on the other node. However, in this technique, recovery of data when the key is lost or broken is not considered as in the case of the first related art.
As explained above, the related arts have been intended to realize backup and recovery of electronic information in the condition that it is concealed by encryption. However, the related explained above is accompanied by a problem that loss or breakdown of device storing electronic information including a key information cannot be covered because it is not considered to recover the encrypted backup information when the key information used for encryption is lost.
Moreover, even when a key used for decoding the encryption to cover the problem explained above can be simply backed up, a measure for illegal action to deteriorate reliability for backup management of key such as conspiracy by the server keeping the key and the server keeping the encrypted electronic value information must be considered.